1. Field of the Invention
The present invention relates to an electric actuator system for driving a movable member, such as an air mix door or a mode switch door, in a vehicle air conditioning system.
2. Description of the Related Art
Generally, electric actuators, when activated, move to a preset operation limit defined by mechanical restriction means such as a stopper so that the operation angle of the actuator is controlled relative to this limit as a starting point. Moving the actuator to a starting point and storing the position of the starting point will be hereinafter termed generally as “initialization.” One problem in such an initialization procedure occurs when the actuator moves to the limit position by moving a rotatable lever of the actuator until it hits a stopper. Such an impact sometimes causes deflection in the stopper, which leads to variations in the recognized starting point.
The applicants of the present invention have shown, in a previously filed application (Japanese Patent Application No. 2002-171563), an arrangement in which the lever strikes a plurality of stoppers provided in a unit case to disperse the striking impact. While this structure reduces the variations in the starting point position, there is still the problem of deflection in the stoppers.
It was discovered that because each unit case in which the stoppers are mounted has a different rigidity, which causes variations in the amount of deflection in the stoppers, correction of the operation angle of the actuator using an electronic control unit based on a previously measured amount of deflection of each stopper became necessary. In such control, the correction value for the operation angle would have to be different for each case because of variations in the amount of deflection in each of the stoppers themselves. That is to say, one common control unit could not be used for the control of several actuators.
Another problem occurs if the actuator is left for some time in a locked condition such as when the battery for supplying power to the actuator is dismounted by chance when the actuator has been locked by the mechanical restriction means during initialization. There is the possibility that the gear strength, stoppers and the like built in the actuator may deteriorate because of creep.
Meanwhile, in recent years, more and more vehicles have a control system that stops the supply of power from the battery to the vehicle's electrical systems after a preset period of time has passed after the ignition switch is turned off. This is to suppress consumption of energy caused by dark current from the battery to electrical systems when the vehicle is stopped or parked, i.e., when the ignition switch is off.
While a memory device in the electric actuator system retains data on the starting point as long as it is powered, the data vanishes when the supply of power is stopped. The system thus carries out initialization again when it is started the next time.
This means that initialization is necessary almost every time the ignition switch is turned on, because even though the battery is not removed, the starting point data retained in the memory device disappears after the lapse of a preset time period following the turning off of the ignition switch. Additionally, the case in which the battery has been removed whereby power supply to the memory device is stopped must be considered. Such frequent operation of the actuator may result in wear of brushes in the pulse generator or electric motor, leading to shortened life of the actuator.